Hydroformylation reactions wherein olefinic substrates are reacted with carbon monoxide and hydrogen to form an aldehyde are known in the art and provide important building blocks for the petrochemical industry.
One of the early processes for producing acrylic acid was the Reppe reaction, which involves the reaction of acetylene with carbon monoxide using a nickel carbonyl catalyst and high pressure. Two inherent disadvantages of using acetylene are high cost and explosion danger.
Other routes included producing beta-propiolactone, starting from ketene, and alcoholysis of acrylonitrile.
Ohara, et al, in "Oxidize Propylene to Acrylics" Hydrocarbon Processing, p. 85-88 (Nov., 1972) discuss the Nipon Shokubai process wherein propylene is oxidized to acrylic acid and esterfied to key acrylic esters. The polyvalent metal oxide catalyst for this reaction, containing predominantly molybdenum was not highly satisfactory with respect to selectivity to acrylic acid and catalyst life. When tellurium oxide was used as a promoter in an attempt to increase selectivity to acrylic acid, it was found the oxide was gradually reduced to tellurium metal.
Another disadvantage of using the process starting with propylene to produce acrylic acid is that acrylic acid has a tendency to polymerize and acrylic acid produced by propylene oxidation tends to have a higher polymerization rate in the recovery and purification steps compared to acrylic acid made by other processes and therefore, polymerization prevention steps have to be incorporated.
In "A New Route to Acrylic Acid", Hydrocarbon Processing p. 95-96 (November 1972), Olivier, et al. disclose a new route to acrylic acid which uses ethylene in place of acetylene. Under anhydrous conditions ethylene reacts with carbon monoxide and oxygen in a titanium-clad reactor with a palladium-copper catalyst, in acetic acid solution to form a mixture of acrylic acid and .beta.-acetoxypropionic acid. In this process the reaction medium must constantly be kept anhydrous and requires the use of a drying agent which is most commonly acetic anhydride.
In the practice of this process, the concentration of anhydride has a marked effect on both reaction rate and relative selectivity to acrylic acid. In addition it is necessary to carry out the reaction in a high boiling point acid to facilitate recovery of acrylic acid. However, if the high boiling point acid is used as the only solvent, it can reduce the rate of the reaction.
In an article on hydroformylation by R. L. Pruett in Adv. Organometallic Chem., 17, p. 1 (1979) there is a discussion of the background of hydroformylation reactions, including commercial utilization, substrates, catalysts, products and reaction mechanisms.
G Krsek and H. Adkins reported in J. Am. Chem. Soc. 71, 3051 (1949) that n-butyl vinyl ether was hydroformylated by the use of cobalt carbonyl catalyst, which gave low yields of products (.about.31%) with the formyl groups exclusively in the .alpha. position.
Acrylic vinyl ethers, such as dihydropyran and its derivatives, were hydroformylated with a cobalt catalyst at high temperature and pressure (180 psi and 300 atm of CO/H.sub.2 1:2), in a process reported by Falbe and Korte, Chem. Ber. 97, 1104 (1964).
In U.S. Pat. No. 2,497,303, W. F. Gresham et al. disclosed the cobalt hydroformylation of methyl vinyl ether at the conditions of 160.degree.-175.degree. C. and 645.about. 720 atm to give 3-methoxypropionaldehyde.
A review article, "Synthesis of Intermediates by Rhodium-Catalyzed Hydroformylation" of Angew. Chem. Int. Ed. Engl. 19, 178-183 (1980) by H. Siegel and W. Himmele reported the hydroformylation of 2-aryloxypropanal synthesis from aryl vinyl. Similar results were also reported by J. M. Brown, Chemistry and Industry (Oct. 2 1982) pp. 737.
The use of carbonylhydridotris(triphenylphosphine) rhodium(I) for hydroformylation of various olefinic substrates and its mechanism was reviewed by F. H. Jardine, Polyhedron Vol. 1, No. 7-8, pp. 569-605 (1982).
The importance of the use of various phosphine ligands in combination with a rhodium hydroformylation catalyst for functionalized olefins, such as vinyl acetate, allyl acetate, 3-butenyl acetate, ethyl acrylate, allyl alcohol, allyl butyl ether and 3-butenyl butyl ether, has been examined. But the reaction of vinyl ether using a rhodium catalyst has still remained unreported.
U.S. Pat. No. 4,072,709, issued to Monsanto Company discloses a hydroformylation/oxidation process to produce alphaacetoxy-propionaldehyde from vinyl ester. The hydroformylation of vinyl ester has also been reported by J. Mol. Cat. 18 (1983), 381-390, J. Mol. Cat. 2 (1977) 301-306, DT 2504-981 and Fr. Demande FR 2,477,140.
Another discussion of hydroformylation is presented in "Hydroformylation, Oxo Synthesis, Roelen Reaction" by J. Falbe, New Synthesis with Carbon Monoxide, (1980).
It would be a considerable advance in the art to devise a novel method for synthesis of acrylic acid intermediate products which demonstrates improved conversion and yields, employs a catalyst with increased activity and uses mild reaction conditions.